Data is stored on magnetic media by writing on the media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, hard disk, or the like. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Conventional thin film read heads employ magnetoresistive material, generally formed in a layered structure of magnetoresistive and non-magnetoresistive materials, to detect the magnetic moment of the bit on the media. A sensing current is passed through the magnetoresistive material to detect changes in the resistance of the material induced by the bits as the media is moved with respect to the read head.
The magnetoresistive effect, given by AR/R, may be detected by passing a sensing current through the sensor along the plane of the layers, or by passing current through the sensor perpendicular to the plane of the layers. By passing the sensing current perpendicular rather than parallel to the plane, shunt current through non-magnetoresistive layers of the sensor can be eliminated, thus improving the magnetoresistive effect.
Current perpendicular-to-the-plane devices or CPP devices may have a giant magnetoresistive multilayer, a spin tunneling junction, a spin valve, or other stacked type sensor device. For example, U.S. Pat. No. 5,668,688, by Dykes et al., entitled CURRENT PERPENDICULAR-TO-THE-PLANE SPIN VALVE TYPE MAGNETORESISTIVE TRANSDUCER, issued on Sep. 16, 1997, herein incorporated by reference in its entirety, discloses a possible CPP device.
CPP devices while overcoming some problems associated with the current in the plane or CIP devices, have other design problems. For example, U.S. Patent entitled MAGNETORESISTIVE TRANSDUCER WITH FOUR-LEAD CONTACT, by David Richardson, et al., Ser. No. 09/006,307, filed on Jan. 13, 1998, issued as U.S. Pat. No. 5,959,811 on Sep. 28, 1999, herein incorporated by reference in its entirety, describes problems associated with providing electrical contacts to the magnetoresistive sensors. With CPP devices, because the thin film layers have such a low resistance perpendicular to their plane, the resistance of the sensing leads significantly reduces the magnetoresistive effect of the device. Thus, it is important to minimize the resistance of the leads. As such, the leads typically are formed of low resistance conductive materials, such as Au, Ag, Al, Cu, or the like.
Low resistance lead materials, on the other hand, have been observed by the present inventors to create another problem in CPP devices. Because the magnetoresistive stack typically is formed on the lead material, the lead material is partially etched when defining the magnetoresistive stack. This causes lead material to redeposit on the side walls of the magnetoresistive stack. This is particularly true at small geometries.
The redeposited lead material creates a shunt path around the layers which significantly reduces the magnetoresistive effect. Due to the smaller path length, such current shunting is even more detrimental in CPP devices than in than the current shunting that occurs along the layers of CIP devices. Thus, while low resistance leads are necessary for optimizing the magnetoresistive effect, their redeposition on the side wall can significantly reduce the magnetoresistive effect by providing a low resistance shunt path around the stack.